rc80211_pid_algo.c

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/*
 * Copyright 2002-2005, Instant802 Networks, Inc.
 * Copyright 2005, Devicescape Software, Inc.
 * Copyright 2007, Mattias Nissler <[email protected]>
 * Copyright 2007-2008, Stefano Brivio <[email protected]>
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License version 2 as
 * published by the Free Software Foundation.
 */

#include <linux/netdevice.h>
#include <linux/types.h>
#include <linux/skbuff.h>
#include <linux/debugfs.h>
#include <linux/slab.h>
#include <net/mac80211.h>
#include "rate.h"
#include "mesh.h"
#include "rc80211_pid.h"


/* This is an implementation of a TX rate control algorithm that uses a PID
 * controller. Given a target failed frames rate, the controller decides about
 * TX rate changes to meet the target failed frames rate.
 *
 * The controller basically computes the following:
 *
 * adj = CP * err + CI * err_avg + CD * (err - last_err) * (1 + sharpening)
 *
 * where
 *  adj adjustment value that is used to switch TX rate (see below)
 *  err current error: target vs. current failed frames percentage
 *  last_err    last error
 *  err_avg average (i.e. poor man's integral) of recent errors
 *  sharpening  non-zero when fast response is needed (i.e. right after
 *          association or no frames sent for a long time), heading
 *          to zero over time
 *  CP  Proportional coefficient
 *  CI  Integral coefficient
 *  CD  Derivative coefficient
 *
 * CP, CI, CD are subject to careful tuning.
 *
 * The integral component uses a exponential moving average approach instead of
 * an actual sliding window. The advantage is that we don't need to keep an
 * array of the last N error values and computation is easier.
 *
 * Once we have the adj value, we map it to a rate by means of a learning
 * algorithm. This algorithm keeps the state of the percentual failed frames
 * difference between rates. The behaviour of the lowest available rate is kept
 * as a reference value, and every time we switch between two rates, we compute
 * the difference between the failed frames each rate exhibited. By doing so,
 * we compare behaviours which different rates exhibited in adjacent timeslices,
 * thus the comparison is minimally affected by external conditions. This
 * difference gets propagated to the whole set of measurements, so that the
 * reference is always the same. Periodically, we normalize this set so that
 * recent events weigh the most. By comparing the adj value with this set, we
 * avoid pejorative switches to lower rates and allow for switches to higher
 * rates if they behaved well.
 *
 * Note that for the computations we use a fixed-point representation to avoid
 * floating point arithmetic. Hence, all values are shifted left by
 * RC_PID_ARITH_SHIFT.
 */


/* Adjust the rate while ensuring that we won't switch to a lower rate if it
 * exhibited a worse failed frames behaviour and we'll choose the highest rate
 * whose failed frames behaviour is not worse than the one of the original rate
 * target. While at it, check that the new rate is valid. */
static void rate_control_pid_adjust_rate(struct ieee80211_supported_band *sband,
                     struct ieee80211_sta *sta,
                     struct rc_pid_sta_info *spinfo, int adj,
                     struct rc_pid_rateinfo *rinfo)
{
    int cur_sorted, new_sorted, probe, tmp, n_bitrates, band;
    int cur = spinfo->txrate_idx;

    band = sband->band;
    n_bitrates = sband->n_bitrates;

    /* Map passed arguments to sorted values. */
    cur_sorted = rinfo[cur].rev_index;
    new_sorted = cur_sorted + adj;

    /* Check limits. */
    if (new_sorted < 0)
        new_sorted = rinfo[0].rev_index;
    else if (new_sorted >= n_bitrates)
        new_sorted = rinfo[n_bitrates - 1].rev_index;

    tmp = new_sorted;

    if (adj < 0) {
        /* Ensure that the rate decrease isn't disadvantageous. */
        for (probe = cur_sorted; probe >= new_sorted; probe--)
            if (rinfo[probe].diff <= rinfo[cur_sorted].diff &&
                rate_supported(sta, band, rinfo[probe].index))
                tmp = probe;
    } else {
        /* Look for rate increase with zero (or below) cost. */
        for (probe = new_sorted + 1; probe < n_bitrates; probe++)
            if (rinfo[probe].diff <= rinfo[new_sorted].diff &&
                rate_supported(sta, band, rinfo[probe].index))
                tmp = probe;
    }

    /* Fit the rate found to the nearest supported rate. */
    do {
        if (rate_supported(sta, band, rinfo[tmp].index)) {
            spinfo->txrate_idx = rinfo[tmp].index;
            break;
        }
        if (adj < 0)
            tmp--;
        else
            tmp++;
    } while (tmp < n_bitrates && tmp >= 0);

#ifdef CONFIG_MAC80211_DEBUGFS
    rate_control_pid_event_rate_change(&spinfo->events,
        spinfo->txrate_idx,
        sband->bitrates[spinfo->txrate_idx].bitrate);
#endif
}

/* Normalize the failed frames per-rate differences. */
static void rate_control_pid_normalize(struct rc_pid_info *pinfo, int l)
{
    int i, norm_offset = pinfo->norm_offset;
    struct rc_pid_rateinfo *r = pinfo->rinfo;

    if (r[0].diff > norm_offset)
        r[0].diff -= norm_offset;
    else if (r[0].diff < -norm_offset)
        r[0].diff += norm_offset;
    for (i = 0; i < l - 1; i++)
        if (r[i + 1].diff > r[i].diff + norm_offset)
            r[i + 1].diff -= norm_offset;
        else if (r[i + 1].diff <= r[i].diff)
            r[i + 1].diff += norm_offset;
}

static void rate_control_pid_sample(struct rc_pid_info *pinfo,
                    struct ieee80211_supported_band *sband,
                    struct ieee80211_sta *sta,
                    struct rc_pid_sta_info *spinfo)
{
    struct rc_pid_rateinfo *rinfo = pinfo->rinfo;
    u32 pf;
    s32 err_avg;
    u32 err_prop;
    u32 err_int;
    u32 err_der;
    int adj, i, j, tmp;
    unsigned long period;

    /* In case nothing happened during the previous control interval, turn
     * the sharpening factor on. */
    period = msecs_to_jiffies(pinfo->sampling_period);
    if (jiffies - spinfo->last_sample > 2 * period)
        spinfo->sharp_cnt = pinfo->sharpen_duration;

    spinfo->last_sample = jiffies;

    /* This should never happen, but in case, we assume the old sample is
     * still a good measurement and copy it. */
    if (unlikely(spinfo->tx_num_xmit == 0))
        pf = spinfo->last_pf;
    else
        pf = spinfo->tx_num_failed * 100 / spinfo->tx_num_xmit;

    spinfo->tx_num_xmit = 0;
    spinfo->tx_num_failed = 0;

    /* If we just switched rate, update the rate behaviour info. */
    if (pinfo->oldrate != spinfo->txrate_idx) {

        i = rinfo[pinfo->oldrate].rev_index;
        j = rinfo[spinfo->txrate_idx].rev_index;

        tmp = (pf - spinfo->last_pf);
        tmp = RC_PID_DO_ARITH_RIGHT_SHIFT(tmp, RC_PID_ARITH_SHIFT);

        rinfo[j].diff = rinfo[i].diff + tmp;
        pinfo->oldrate = spinfo->txrate_idx;
    }
    rate_control_pid_normalize(pinfo, sband->n_bitrates);

    /* Compute the proportional, integral and derivative errors. */
    err_prop = (pinfo->target - pf) << RC_PID_ARITH_SHIFT;

    err_avg = spinfo->err_avg_sc >> pinfo->smoothing_shift;
    spinfo->err_avg_sc = spinfo->err_avg_sc - err_avg + err_prop;
    err_int = spinfo->err_avg_sc >> pinfo->smoothing_shift;

    err_der = (pf - spinfo->last_pf) *
          (1 + pinfo->sharpen_factor * spinfo->sharp_cnt);
    spinfo->last_pf = pf;
    if (spinfo->sharp_cnt)
            spinfo->sharp_cnt--;

#ifdef CONFIG_MAC80211_DEBUGFS
    rate_control_pid_event_pf_sample(&spinfo->events, pf, err_prop, err_int,
                     err_der);
#endif

    /* Compute the controller output. */
    adj = (err_prop * pinfo->coeff_p + err_int * pinfo->coeff_i
          + err_der * pinfo->coeff_d);
    adj = RC_PID_DO_ARITH_RIGHT_SHIFT(adj, 2 * RC_PID_ARITH_SHIFT);

    /* Change rate. */
    if (adj)
        rate_control_pid_adjust_rate(sband, sta, spinfo, adj, rinfo);
}

static void rate_control_pid_tx_status(void *priv, struct ieee80211_supported_band *sband,
                       struct ieee80211_sta *sta, void *priv_sta,
                       struct sk_buff *skb)
{
    struct rc_pid_info *pinfo = priv;
    struct rc_pid_sta_info *spinfo = priv_sta;
    unsigned long period;
    struct ieee80211_tx_info *info = IEEE80211_SKB_CB(skb);

    if (!spinfo)
        return;

    /* Ignore all frames that were sent with a different rate than the rate
     * we currently advise mac80211 to use. */
    if (info->status.rates[0].idx != spinfo->txrate_idx)
        return;

    spinfo->tx_num_xmit++;

#ifdef CONFIG_MAC80211_DEBUGFS
    rate_control_pid_event_tx_status(&spinfo->events, info);
#endif

    /* We count frames that totally failed to be transmitted as two bad
     * frames, those that made it out but had some retries as one good and
     * one bad frame. */
    if (!(info->flags & IEEE80211_TX_STAT_ACK)) {
        spinfo->tx_num_failed += 2;
        spinfo->tx_num_xmit++;
    } else if (info->status.rates[0].count > 1) {
        spinfo->tx_num_failed++;
        spinfo->tx_num_xmit++;
    }

    /* Update PID controller state. */
    period = msecs_to_jiffies(pinfo->sampling_period);
    if (time_after(jiffies, spinfo->last_sample + period))
        rate_control_pid_sample(pinfo, sband, sta, spinfo);
}

static void
rate_control_pid_get_rate(void *priv, struct ieee80211_sta *sta,
              void *priv_sta,
              struct ieee80211_tx_rate_control *txrc)
{
    struct sk_buff *skb = txrc->skb;
    struct ieee80211_supported_band *sband = txrc->sband;
    struct ieee80211_tx_info *info = IEEE80211_SKB_CB(skb);
    struct rc_pid_sta_info *spinfo = priv_sta;
    int rateidx;

    if (txrc->rts)
        info->control.rates[0].count =
            txrc->hw->conf.long_frame_max_tx_count;
    else
        info->control.rates[0].count =
            txrc->hw->conf.short_frame_max_tx_count;

    /* Send management frames and NO_ACK data using lowest rate. */
    if (rate_control_send_low(sta, priv_sta, txrc))
        return;

    rateidx = spinfo->txrate_idx;

    if (rateidx >= sband->n_bitrates)
        rateidx = sband->n_bitrates - 1;

    info->control.rates[0].idx = rateidx;

#ifdef CONFIG_MAC80211_DEBUGFS
    rate_control_pid_event_tx_rate(&spinfo->events,
        rateidx, sband->bitrates[rateidx].bitrate);
#endif
}

static void
rate_control_pid_rate_init(void *priv, struct ieee80211_supported_band *sband,
               struct ieee80211_sta *sta, void *priv_sta)
{
    struct rc_pid_sta_info *spinfo = priv_sta;
    struct rc_pid_info *pinfo = priv;
    struct rc_pid_rateinfo *rinfo = pinfo->rinfo;
    int i, j, tmp;
    bool s;

    /* TODO: This routine should consider using RSSI from previous packets
     * as we need to have IEEE 802.1X auth succeed immediately after assoc..
     * Until that method is implemented, we will use the lowest supported
     * rate as a workaround. */

    /* Sort the rates. This is optimized for the most common case (i.e.
     * almost-sorted CCK+OFDM rates). Kind of bubble-sort with reversed
     * mapping too. */
    for (i = 0; i < sband->n_bitrates; i++) {
        rinfo[i].index = i;
        rinfo[i].rev_index = i;
        if (RC_PID_FAST_START)
            rinfo[i].diff = 0;
        else
            rinfo[i].diff = i * pinfo->norm_offset;
    }
    for (i = 1; i < sband->n_bitrates; i++) {
        s = false;
        for (j = 0; j < sband->n_bitrates - i; j++)
            if (unlikely(sband->bitrates[rinfo[j].index].bitrate >
                     sband->bitrates[rinfo[j + 1].index].bitrate)) {
                tmp = rinfo[j].index;
                rinfo[j].index = rinfo[j + 1].index;
                rinfo[j + 1].index = tmp;
                rinfo[rinfo[j].index].rev_index = j;
                rinfo[rinfo[j + 1].index].rev_index = j + 1;
                s = true;
            }
        if (!s)
            break;
    }

    spinfo->txrate_idx = rate_lowest_index(sband, sta);
}

static void *rate_control_pid_alloc(struct ieee80211_hw *hw,
                    struct dentry *debugfsdir)
{
    struct rc_pid_info *pinfo;
    struct rc_pid_rateinfo *rinfo;
    struct ieee80211_supported_band *sband;
    int i, max_rates = 0;
#ifdef CONFIG_MAC80211_DEBUGFS
    struct rc_pid_debugfs_entries *de;
#endif

    pinfo = kmalloc(sizeof(*pinfo), GFP_ATOMIC);
    if (!pinfo)
        return NULL;

    for (i = 0; i < IEEE80211_NUM_BANDS; i++) {
        sband = hw->wiphy->bands[i];
        if (sband && sband->n_bitrates > max_rates)
            max_rates = sband->n_bitrates;
    }

    rinfo = kmalloc(sizeof(*rinfo) * max_rates, GFP_ATOMIC);
    if (!rinfo) {
        kfree(pinfo);
        return NULL;
    }

    pinfo->target = RC_PID_TARGET_PF;
    pinfo->sampling_period = RC_PID_INTERVAL;
    pinfo->coeff_p = RC_PID_COEFF_P;
    pinfo->coeff_i = RC_PID_COEFF_I;
    pinfo->coeff_d = RC_PID_COEFF_D;
    pinfo->smoothing_shift = RC_PID_SMOOTHING_SHIFT;
    pinfo->sharpen_factor = RC_PID_SHARPENING_FACTOR;
    pinfo->sharpen_duration = RC_PID_SHARPENING_DURATION;
    pinfo->norm_offset = RC_PID_NORM_OFFSET;
    pinfo->rinfo = rinfo;
    pinfo->oldrate = 0;

#ifdef CONFIG_MAC80211_DEBUGFS
    de = &pinfo->dentries;
    de->target = debugfs_create_u32("target_pf", S_IRUSR | S_IWUSR,
                    debugfsdir, &pinfo->target);
    de->sampling_period = debugfs_create_u32("sampling_period",
                         S_IRUSR | S_IWUSR, debugfsdir,
                         &pinfo->sampling_period);
    de->coeff_p = debugfs_create_u32("coeff_p", S_IRUSR | S_IWUSR,
                     debugfsdir, (u32 *)&pinfo->coeff_p);
    de->coeff_i = debugfs_create_u32("coeff_i", S_IRUSR | S_IWUSR,
                     debugfsdir, (u32 *)&pinfo->coeff_i);
    de->coeff_d = debugfs_create_u32("coeff_d", S_IRUSR | S_IWUSR,
                     debugfsdir, (u32 *)&pinfo->coeff_d);
    de->smoothing_shift = debugfs_create_u32("smoothing_shift",
                         S_IRUSR | S_IWUSR, debugfsdir,
                         &pinfo->smoothing_shift);
    de->sharpen_factor = debugfs_create_u32("sharpen_factor",
                           S_IRUSR | S_IWUSR, debugfsdir,
                           &pinfo->sharpen_factor);
    de->sharpen_duration = debugfs_create_u32("sharpen_duration",
                          S_IRUSR | S_IWUSR, debugfsdir,
                          &pinfo->sharpen_duration);
    de->norm_offset = debugfs_create_u32("norm_offset",
                         S_IRUSR | S_IWUSR, debugfsdir,
                         &pinfo->norm_offset);
#endif

    return pinfo;
}

static void rate_control_pid_free(void *priv)
{
    struct rc_pid_info *pinfo = priv;
#ifdef CONFIG_MAC80211_DEBUGFS
    struct rc_pid_debugfs_entries *de = &pinfo->dentries;

    debugfs_remove(de->norm_offset);
    debugfs_remove(de->sharpen_duration);
    debugfs_remove(de->sharpen_factor);
    debugfs_remove(de->smoothing_shift);
    debugfs_remove(de->coeff_d);
    debugfs_remove(de->coeff_i);
    debugfs_remove(de->coeff_p);
    debugfs_remove(de->sampling_period);
    debugfs_remove(de->target);
#endif

    kfree(pinfo->rinfo);
    kfree(pinfo);
}

static void *rate_control_pid_alloc_sta(void *priv, struct ieee80211_sta *sta,
                    gfp_t gfp)
{
    struct rc_pid_sta_info *spinfo;

    spinfo = kzalloc(sizeof(*spinfo), gfp);
    if (spinfo == NULL)
        return NULL;

    spinfo->last_sample = jiffies;

#ifdef CONFIG_MAC80211_DEBUGFS
    spin_lock_init(&spinfo->events.lock);
    init_waitqueue_head(&spinfo->events.waitqueue);
#endif

    return spinfo;
}

static void rate_control_pid_free_sta(void *priv, struct ieee80211_sta *sta,
                      void *priv_sta)
{
    kfree(priv_sta);
}

static struct rate_control_ops mac80211_rcpid = {
    .name = "pid",
    .tx_status = rate_control_pid_tx_status,
    .get_rate = rate_control_pid_get_rate,
    .rate_init = rate_control_pid_rate_init,
    .alloc = rate_control_pid_alloc,
    .free = rate_control_pid_free,
    .alloc_sta = rate_control_pid_alloc_sta,
    .free_sta = rate_control_pid_free_sta,
#ifdef CONFIG_MAC80211_DEBUGFS
    .add_sta_debugfs = rate_control_pid_add_sta_debugfs,
    .remove_sta_debugfs = rate_control_pid_remove_sta_debugfs,
#endif
};

int __init rc80211_pid_init(void)
{
    return ieee80211_rate_control_register(&mac80211_rcpid);
}

void rc80211_pid_exit(void)
{
    ieee80211_rate_control_unregister(&mac80211_rcpid);
}